a. Field of the Invention
The present invention pertains to testing of networks specifically to testing networks that have different upstream and downstream paths.
b. Description of the Background
Networks that are deployed in the field have performance characteristics that are difficult to accurately measure or simulate in a lab environment. Various components that make up the transmission network and the devices that are connected thereto cannot be easily subjected to ‘real world’ environments in a test laboratory.
For example, in order to test the upstream performance of a cable modem or other home terminal device connected to a cable television distribution network, it would be desirable to connect the cable modem at a subscriber's home. To generate performance characteristics, a signal is transmitted through the network and measured to determine any lost or corrupted data packets, audible impairments in phone conversations, high bit error rates, high latency, low throughput, or other characteristics. Some of the test equipment requires that both ends of the connection be located in the same physical location for testing. Such connections may be cumbersome to accomplish using existing equipment when performed in the field, as a separate signal path may need to be established at a subscriber's home for the sake of the test equipment.
Other testing methodologies rely on testing devices in a laboratory environment with artificially generated noise profiles. While such noise profiles may assist a designer in preliminary characterization of a device, some phenomena may not be able to be characterized in a laboratory environment.
In another use for testing methods, the network performance may be characterized. Such information may be useful in identifying areas for maintenance or for planning upgrades to the network.
Some transmission networks, such as cable television distribution networks, have a significant difference in the upstream and downstream performance characteristics. In general, the downstream performance is relatively noise free, while the upstream performance is significantly noisier. The downstream performance is generally well characterized and maintained, as subscribers are quick to report any problems with their television reception. The upstream performance is much less noticeable and the upstream direction may have much different and larger impairments than the downstream signal path.
Cable upstream plant impairments can be classified into two general categories. Additive impairments are noise signals that are linearly summed with the desired signal. Some additive impairments are random noise, burst noise, common path distortion, ingressing broadcast carriers, and switching regulator noise. Multiplicative impairments are distortions that occur to the signal being transmitted. Some multiplicative impairments are group delay distortion, multipath distortion, laser clipping, and hum modulation. A key difference is that additive impairments can be observed at the hub without a signal transmission occurring, but the multiplicative impairments cannot be observed without a signal transmission occurring.
It would therefore be advantageous to provide a system and method for testing networks and components attached to networks wherein the testing can use actual distribution paths in the field. It would be further advantageous to provide a system wherein the test equipment may be located in a convenient location and for the system and method to be capable of gathering data about actual network performance.